Electric Motor Driving System, Electric Four-Wheel Drive Vehicle, and Hybrid Vehicle

ABSTRACT

An electric four-wheel drive vehicle includes: an internal combustion engine; a generator for outputting DC electrical power; an inverter for converting DC electrical power, output from the generator, into AC electrical power; and an AC electric motor, which is driven by the inverter, for driving rear wheels. An electric motor controller controls the inverter, the AC electric motor, and the generator, according to torque instructions from a vehicle. Furthermore, in a case that the output of the AC electric motor becomes negative, and excess electrical energy is generated, the electric motor controller controls the current applied to said AC electric motor such that the loss in said AC electric motor exceeds the negative output of said AC electric motor. This enables the AC electric motor to absorb excess electrical energy in the form of thermal loss.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electric motor drive system, anelectric four-wheel drive vehicle, and a hybrid vehicle, andparticularly to an electric motor control system for controlling agenerator and electric motor, and an electric four-wheel drive vehicleand hybrid vehicle including such an electric motor control system.

2. Description of the Related Art

As a control device for a hybrid vehicle, a series hybrid vehicle isknown as disclosed in JP-A-11-332007, for example. The aforementionedseries hybrid vehicle has a configuration in which an output shaft of anengine is mechanically separated from a vehicle driving shaft. With sucha configuration, the electrical energy generated by a generator drivenby the engine is supplied to a driving electric motor, and the vehicleis driven using the output torque.

Also, a hybrid vehicle is known, which has a battery for temporarilystoring generated electrical power and regenerative electrical power, asdisclosed in JP-A-11-332007. With such an arrangement, at the time ofcontrolling the vehicle speed or braking the vehicle, the drivinggenerator is used as a regenerative brake, and the regenerative energygenerated in this stage is stored in the battery, thereby enabling theenergy generated in the reduction of the vehicle speed to be effectivelyused. On the other hand, it is known that in a case where the batteryfor absorbing the regenerative energy is almost fully charged, theregenerative electrical power continuously generated by the drivinggenerator leads to overcharge of the battery. In order to prevent such asituation, a technique is known that in a case of the battery beingalmost fully charged, the generator is operated in the power-runningstate with the rotational resistance of the engine as a load so as toconsume the regenerative current.

Also, another control method is known for consuming excess regenerativeenergy, which can be applied irrespective of whether or not the engineis connected to the generator, as disclosed in JP-A-2003-134602.Specifically, JP-A-2003-134602 discloses a hybrid vehicle having aconfiguration in which in a case that the battery cannot absorb theregenerative energy, the generator is controlled so as to operate withloss of energy, thereby consuming the excess regenerative energy.

SUMMARY OF THE INVENTION

The aforementioned JP-A-11-332007 and JP-A-2003-134602 disclosetechniques in which the regenerative energy generated by the drivingelectric motor in the regeneration operation is stored in the battery,and the generator is controlled so as to consume any excess regenerativeenergy. However, such a technique, in which the excess energy isconsumed by the generator, disclosed in JP-A-11-332007 andJP-A-2003-134602 cannot be applied to a hybrid vehicle employing an ACgenerator as the generator. Furthermore, an electric four-wheel drivevehicle having no battery cannot perform regeneration operation.

It is an object of the present invention to provide: an electric motorcontrol system which has a function of consuming the excess regenerativeenergy, and which can be applied to an electric four-wheel drive vehiclehaving no battery and a hybrid vehicle employing an AC generator as agenerator; an electric four-wheel drive vehicle and hybrid vehicleincluding such an electric motor control system.

(1) In order to solve the aforementioned problems, according to a firstaspect of the present invention, a control system for an electricdriving system is included in an electric driving system for a vehicle.With such an arrangement, the electric driving system for a vehicleincludes: an in-vehicle power supply for supplying DC electrical power;an inverter for converting the DC electrical power output from thein-vehicle power supply, into AC electrical power; and an AC electricmotor, which is driven by the AC electrical power output from theinverter, for generating electrical driving force for driving acomponent to be driven. Furthermore, the control system for an electricdriving system includes control means for controlling driving of the ACelectric motor by controlling the inverter according to an instructedtorque for the AC electric motor. In a case that the output of the ACelectric motor becomes negative, and excess electrical energy isgenerated, the control means control the current applied to the ACelectric motor such that the loss in the AC electric motor exceeds thenegative output of the AC electric motor.

Such an arrangement allows an electric four-wheel drive vehicle havingno battery to consume excess regenerative energy.

(2) With the control system for an electric driving system according tothe aforementioned (1), in a case that the output of the AC electricmotor becomes negative, and excess electrical energy is generated, thecontrol means preferably control the current applied to the AC electricmotor so as to increase ineffective current in the AC electric motor.

(3) With the control system for an electric driving system according tothe aforementioned (2), the ineffective current in the AC electricmotor, which is absorbed in the form of loss in the AC electric motor,is preferably determined based upon the excess electrical power outputto the inverter from the in-vehicle power supply. (4) In order to solvethe aforementioned problems, according to a second aspect of the presentinvention, a control system for an electric driving system, is includedin an electric driving system for a multi-wheel drive vehicle. With suchan arrangement the electric driving system for a multi-wheel drivevehicle includes: a generator for outputting DC electrical power by thedriving force received from an internal combustion engine for driving atleast one of multiple wheels; an inverter for converting the DCelectrical power directly received from the generator, into ACelectrical power; and an AC electric motor, which is driven by the ACelectrical power output from the inverter, for driving at least one ofthe multiple wheels other than the wheels driven by the internalcombustion engine. Furthermore, the control system for an electricdriving system includes control means for controlling driving of the ACelectric motor by controlling the inverter according to an instructedtorque received from a vehicle for the AC electric motor. In a case thatthe output of the AC electric motor becomes negative, and excesselectrical energy is generated, the control means control the currentapplied to the AC electric motor such that the loss in the AC electricmotor exceeds the negative output of the AC electric motor.

Such an arrangement allows an electric four-wheel drive vehicle havingno battery to consume excess regenerative energy.

(5) With the control system for an electric driving system according tothe aforementioned (4), in a case that the output of the AC electricmotor becomes negative, and excess electrical energy is generated, thecontrol means preferably control the current applied to the AC electricmotor so as to increase ineffective current in the AC electric motor.

(6) With the control system for an electric driving system according tothe aforementioned (5), the ineffective current in the AC electricmotor, which is absorbed in the form of loss in the AC electric motor,is preferably determined based upon the excess electrical power outputto the inverter from the generator.

(7) In order to solve the aforementioned problems, according to a thirdaspect of the present invention, a control system for an electricdriving system is included in an electric driving system for an electricvehicle. With such an arrangement, the electric driving system for anelectric vehicle includes: a capacitor which enablescharging/discharging using DC electrical power; an inverter forconverting the DC electrical power received by discharging thecapacitor, into AC electrical power; and an AC electric motor, which isdriven by the AC electrical power output from the inverter, forgenerating electrical driving force for driving the vehicle.Furthermore, the control system for an electric driving system includescontrol means for controlling driving of the AC electric motor bycontrolling the inverter according to an instructed torque received froma vehicle for the AC electric motor. In a case that the output of the ACelectric motor becomes negative, and excess electrical energy isgenerated, the control means control the current applied to the ACelectric motor such that the loss in the AC electric motor exceeds thenegative output of the AC electric motor.

Such an arrangement allows an electric four-wheel drive vehicle havingno battery to consume excess regenerative energy.

(8) With the control system for an electric driving system according tothe aforementioned (7), in a case that the output of the AC electricmotor becomes negative, and excess electrical energy is generated, thecontrol means preferably control the current applied to the AC electricmotor so as to increase ineffective current in the AC electric motor.

(9) With the control system for an electric driving system according tothe aforementioned (8), the ineffective current in the AC electricmotor, which is absorbed in the form of loss in the AC electric motor,is preferably determined based upon the excess electrical power outputto the inverter from the capacitor. (10) In order to solve theaforementioned problems, according to a fourth aspect of the presentinvention, an electric driving system for a vehicle, for generatingelectrical driving force for driving a component of the vehicle to bedriven, comprises: an in-vehicle power supply for supplying DCelectrical power; an inverter for converting the DC electrical power,output from the in-vehicle power supply, into AC electrical power; an ACelectric motor, which is driven by the AC electrical power output fromthe inverter, for generating electrical driving force; and a controlunit for controlling driving of the AC electric motor by controlling theinverter according to an instructed torque for the AC electric motor.With such an arrangement, in a case that the output of the AC electricmotor becomes negative, and excess electrical energy is generated, thecontrol unit controls the current applied to the AC electric motor suchthat the loss in the AC electric motor exceeds the negative output ofthe AC electric motor. In this case, the excess electrical power issupplied to the inverter from the in-vehicle power supply in the form ofloss in the AC electric motor.

Such an arrangement allows an electric four-wheel drive vehicle havingno battery to consume excess regenerative energy.

(11) With the electric driving system for a vehicle according to theaforementioned (10), in a case that the output of the AC electric motorbecomes negative, and excess electrical energy is generated, the controlmeans preferably control the current applied to the AC electric motor soas to increase ineffective current in the AC electric motor.

(12) With the electric driving system for a vehicle according to theaforementioned (11), the ineffective current in the AC electric motor ispreferably determined based upon the excess electrical power.

(13) In order to solve the aforementioned problems, according to a fifthaspect of the present invention, an electric driving system for amulti-wheel drive vehicle having a function of driving at least one ofmultiple wheels by an internal combustion engine, and a function ofdriving at least one of the multiple wheels other than the wheels drivenby the internal combustion engine, by electrical driving force,comprises: a generator for outputting DC electrical power by the drivingforce received from the internal combustion engine; an inverter forconverting the DC electrical power directly received from the generator,into AC electrical power; an AC electric motor, which is driven by theAC electrical power output from the inverter, for driving at least oneof the multiple wheels other than the wheels driven by the internalcombustion engine; and a control device including control means forcontrolling driving of the AC electric motor by controlling the inverteraccording to an instructed torque received from a vehicle for the ACelectric motor. With such an arrangement, in a case that the output ofthe AC electric motor becomes negative, and excess electrical energy isgenerated, the control means control the current applied to the ACelectric motor such that the loss in the AC electric motor exceeds thenegative output of the AC electric motor. In this case, the excesselectrical power is supplied to the inverter from the generator in theform of loss in the AC electric motor.

Such an arrangement allows an electric four-wheel drive vehicle havingno battery to consume excess regenerative energy.

(14) With the electric driving system according to the aforementioned(13), in a case that the output of the AC electric motor becomesnegative, and excess electrical energy is generated, the control meanspreferably control the current applied to the AC electric motor so as toincrease ineffective current in the AC electric motor.

(15) With the electric driving system according to the aforementioned(14), the ineffective current in the AC electric motor is preferablydetermined based upon the excess electrical power.

(16) In order to solve the aforementioned problems, according to a sixthaspect of the present invention, an electric driving system for drivinga vehicle by electrical driving force comprises: a capacitor whichenables charging/discharging using DC electrical power; an inverter forconverting the DC electrical power received by discharging thecapacitor, into AC electrical power; an AC electric motor, which isdriven by the AC electrical power output from the inverter, forgenerating the electrical driving force; and a control device includingcontrol means for controlling driving of the AC electric motor bycontrolling the inverter according to an instructed torque received froma vehicle for the AC electric motor. With such an arrangement, in a casethat the output of the AC electric motor becomes negative, and excesselectrical energy is generated, the control means control the currentapplied to the AC electric motor such that the loss in the AC electricmotor exceeds the negative output of the AC electric motor. In thiscase, the excess electrical power is supplied to the inverter from thecapacitor in the form of loss in the AC electric motor.

Such an arrangement allows an electric four-wheel drive vehicle havingno battery to consume excess regenerative energy.

(17) With the electric driving system according to the aforementioned(16), in a case that the output of the AC electric motor becomesnegative, and excess electrical energy is generated, the control meanspreferably control the current applied to the AC electric motor so as toincrease ineffective current in the AC electric motor.

(18) With the electric driving system according to the aforementioned(17), the ineffective current in the AC electric motor is preferablydetermined based upon the excess electrical power.

(19) In order to solve the aforementioned problems, according to aseventh aspect of the present invention, a multi-wheel drive vehiclecomprises: an internal combustion engine for driving at least one ofmultiple wheels; a generator, which is driven by the internal combustionengine, for outputting DC electrical power; an inverter for convertingthe DC electrical power, directly received from the generator, into ACelectrical power; an AC electric motor, which is driven by the ACelectrical power output from the inverter, for driving at least one ofthe multiple wheels other than the wheels driven by the internalcombustion engine; and a control device including control means forcontrolling driving of the AC electric motor by controlling the inverteraccording to an instructed torque received from a vehicle for the ACelectric motor. With such an arrangement, in a case that the output ofthe AC electric motor becomes negative, and excess electrical energy isgenerated, the control means control the current applied to the ACelectric motor such that the loss in the AC electric motor exceeds thenegative output of the AC electric motor. In this case, the excesselectrical power is supplied to the inverter from the generator in theform of loss in the AC electric motor.

Such an arrangement allows an electric four-wheel drive vehicle havingno battery to consume excess regenerative energy.

(20) In order to solve the aforementioned problems, according to aseventh aspect of the present invention, a hybrid vehicle comprises: aninternal combustion engine for generating driving force for a vehicle;an AC electric motor for generating driving force for the vehicle; acapacitor forming a power supply for the AC electric motor; an inverterfor converting DC electrical power received from the capacitor, into ACelectrical power, which is supplied to the AC electric motor for drivingthe AC electric motor; and a control device including control means forcontrolling driving of the AC electric motor by controlling the inverteraccording to an instructed torque received from a vehicle for the ACelectric motor. With such an arrangement, in a case that the output ofthe AC electric motor becomes negative, and excess electrical energy isgenerated, the control means control the current applied to the ACelectric motor such that the loss in the AC electric motor exceeds thenegative output of the AC electric motor. In this case, the excesselectrical power is supplied to the inverter from the capacitor in theform of loss in the AC electric motor.

Such an arrangement allows an electric four-wheel drive vehicle havingno battery to consume excess regenerative energy.

The present invention provide a technique which enables excessregenerative energy to be consumed in an electric four-wheel drivevehicle having no battery to consume, and a hybrid vehicle having aconfiguration employing an AC generator as a generator motor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a system block diagram which shows an overall configuration inwhich an electric motor control system according to an embodiment of thepresent invention is applied to an electric four-wheel drive vehicleemploying an AC electric motor;

FIG. 2 is a block diagram which shows a configuration of an electricmotor controller which is an electric motor control system according toan embodiment of the present invention;

FIG. 3 is a block diagram which shows a configuration of an electricmotor control unit included in an electric motor control systemaccording to an embodiment of the present invention;

FIG. 4 is a flowchart which shows the operation of an electric motorcontrol unit included in an electric motor control system according toan embodiment of the present invention;

FIG. 5 is an explanatory diagram for describing the rollback N-Tcharacteristic used by an electric motor control system according to anembodiment of the present invention;

FIG. 6 is a flowchart which shows the operation of the capacitor voltageinstruction value Vdc* computation unit included in an electric motorcontrol system according to an embodiment of the present invention;

FIG. 7 is an explanatory diagram for describing the characteristics of agenerator;

FIG. 8 is a block diagram which shows the configuration of a generatorcontrol unit included in an electric motor control system according toan embodiment of the present invention;

FIG. 9 is a flowchart which shows the operation of a generator controlunit included in an electric motor control system according to anembodiment of the present invention;

FIGS. 10A through 10C are timing charts which show the control operationof an electric four-wheel drive vehicle employing an electric motorcontrol system according to an embodiment of the present invention;

FIG. 11 is a system block diagram which shows an overall configurationof an arrangement in which an electric motor control system according toan embodiment of the present invention is applied to a hybrid vehiclehaving a simple configuration employing an AC electric motor and an ACgenerator; and

FIG. 12 is a system block diagram which shows an overall configurationof an arrangement in which an electric motor control system according toan embodiment of the present invention is applied to a hybrid vehicleemploying an AC electric motor and a motor generator.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Description will be made below regarding a configuration and operationof an electric motor control system and an electric four-wheel drivevehicle including such an electric motor control system according to anembodiment of the present invention with reference to FIGS. 1 through10.

First, description will be made regarding a configuration and operationof an arrangement in which an electric motor control system according tothe present embodiment is applied to an electric four-wheel drivevehicle employing an AC electric motor, with reference to FIG. 1.

FIG. 1 is a system block diagram which shows an overall configuration inwhich an electric motor control system according to an embodiment of thepresent invention is applied to an electric four-wheel drive vehicleemploying an AC electric motor.

An electric four-wheel drive vehicle 1 includes an engine 3 and an ACelectric motor 6. The driving force of the engine 3 is transmitted tofront wheels 2 through a transmission 30 and axle shafts 13A, therebydriving the front wheels 2. The output of the engine 3 is controlled byan electronic control throttle 11 which is driven according toinstructions from an engine control unit (ECU) 15. The electroniccontrol throttle 11 includes a throttle opening sensor 12 for detectingthe throttle opening of the electronic control throttle 11. The throttleopening thus detected is acquired by the ECU 15. Furthermore, the ECU 15controls the transmission 30.

The driving force of the AC electric motor 6 is transmitted to rearwheels 5 through a clutch 9, a differential gear 7, and axle shafts 13B,thereby driving the rear wheels 5. Specifically, upon the differentialgear 7 engaging with the clutch 9, the rotational force of the ACelectric motor 6 is distributed to the left and right axle shafts 13B bythe differential gear 7, thereby driving the rear wheels 5. Upon therelease of the clutch 9, the AC electric motor 6 is mechanicallyseparated from the rear wheels 5. In this state, the driving force isnot transmitted to the rear wheels 5.

FIG. 1 shows an arrangement in which the AC electric motor 6 is engagedwith the wheels through a switching mechanism such as the clutch 9 andso forth. Also, an arrangement may be made in which the AC electricmotor 6 is directly connected to the wheels. Note that the electricfour-wheel drive vehicle requires the AC motor 6 to perform over a wideoperational range (rotational range) from a low speed up to a highspeed. For example, let us consider a situation in which the vehicle isdriven so as to escape from deep snow or mud. In this case, theimportant performance is that the vehicle can be driven using the rearwheel torque alone. Furthermore, there is a need to output a largeamount of torque at a low speed. On the other hand, let us consider acase in which the vehicle is driven in the four-wheel drive mode over arange of speeds up to a medium-level speed. In this case, there is aneed to drive the electric motor at an extremely high rotational speed.Accordingly, examples of motor types which can be effectively employedas the AC motor 6 include a permanent magnet synchronous motor and afield-coil synchronous motor, which are generally employed for driving ahybrid vehicle. The field-coil synchronous motor has a function ofreducing the field current in a high-rotational range so as to reducethe magnetic flux. This suppresses the induced voltage, thereby enablingthe electric motor to be driven up to a high-rotational range.

Furthermore, an inverter 8 is provided for discretionary control of therequired driving force of the AC motor 6. Specifically, the inverter 8converts the DC electrical power output from the generator 4 into ACelectrical power, and supplies the AC electrical power thus generated,to the AC electric motor 6. Here, the electrical power is input to theinverter 8 in an extremely pulsed manner due to switching of powerdevices. Accordingly, a capacitor 31 is provided to the inverter 8 forsmoothing such a pulsed electrical power. Note that the inverter 8includes the capacitor 31 therewithin.

The engine 3 is connected to a dedicated generator 4. The AC electricalpower generated by the generator 4 is converted into DC electrical powerwith a diode bridge 10. The inverter 8 converts the DC electrical powerinto AC electrical power, whereby the AC electric motor 6 generatesdriving force. With such an arrangement, the voltage required by the ACelectric motor 6 to generate the required torque is obtained bycontrolling the generator 4. Thus, the AC electric motor 6 is driven bythe output of the generator 4. Here, the generator 4 employed in thepresent embodiment is an AC generator such as an alternator or the like.The generator 4 has a configuration which enables power generationcontrol by adjustment of the field current applied to the field coil. Ingeneral, a combination of the generator 4 having such a configurationand the diode bridge 10 is referred to as “alternator”.

A four-wheel drive controller 32 is connected to other devices throughthe communication means such as the ECU 15 and CAN, or the like. Thefour-wheel drive controller 32 serves as a four-wheel drive system forperforming control processing such as calculation of the torqueinstruction transmitted to the AC electric motor 6 for the rear wheelsbased upon the vehicle information, and so forth. An electric motorcontroller 14 controls the generator 4, inverter 8, and AC electricmotor 6, based upon the engine revolution, torque instruction, voltageapplied to the capacitor 31, the revolution of the AC electric motor 6,and the magnetic pole position, which are obtained from the four-wheeldrive controller 32.

Next, description will be made regarding the configuration and operationof the electric motor controller 14 which is an electric motor controlsystem according to an embodiment of the present invention withreference to FIG. 2.

FIG. 2 is a block diagram which shows the configuration of an electricmotor controller which is an electric motor control system according toan embodiment of the present invention.

As shown in FIG. 2, the electric motor controller ECU 14 comprises anelectric motor control unit 16 for controlling the AC electric motor 6and the inverter 8, and a generator control unit 17 for controlling thegenerator 4. The electric motor control unit 16 controls the AC electricmotor 6 according to the torque instruction received from the four-wheeldrive controller 32, which serves as an upper control unit. The electricmotor control unit 16 includes a rollback determination unit 18, acurrent instruction computation unit 50, and a capacitor voltageinstruction computation unit 51. The generator control unit 17 performspower generation control of the generator 4 for generating electricalpower to be input to the inverter 8 and the AC electric motor 6.Specifically, the generator control unit 17 serves as a capacitorvoltage control unit and a voltage feedback control unit for performingfeedback control of the field voltage instruction C1 (Vgf*) for thefield coil of the generator 4 such that the capacitance voltage Vdcbetween both terminals of the capacitor 31 matches the capacitor voltageinstruction value Vdc* output from the electric motor control unit 16.Detailed description will be made regarding the configuration andoperation of the electric motor control unit 16 and the generatorcontrol unit 17 with reference to FIGS. 3 through 9.

The electric four-wheel drive vehicle having such a configuration shownin FIG. 2 has no battery for absorbing electrical power. Accordingly,the operation control needs to be performed such that the electricalpower generated by the generator, which receives the rotational drivingpower received from the engine, matches the driving energy input to theinverter and the electric motor. Let us consider a case in which theoperation control fails to maintain the balance between the generatedenergy and the driving energy. First, let us consider a case in whichthe generated energy is greater than the driving energy. In this case,the excess electrical power flows into the smoothing capacitor 31,leading to an increase of the voltage of the DC bus. In some cases, theexcess voltage of the DC bus exceeds the permissible value, whichresults in damage to the power devices included in the capacitor 31 andthe inverter 8. Conversely, let us consider a case in which thegenerated energy is smaller than the driving energy. In this case, theinsufficient electrical power stored in the capacitor 31 is exhausted bythe inverter and the electric motor, leading to reduction in the voltagethereof. This leads to a problem situation in which the required torquecannot be output. Accordingly, in a system which does not have abattery, it is important to control the generated energy and the drivingenergy with a proper balance therebetween. Furthermore, the same can besaid of a hybrid vehicle having a battery in a case of the battery beingalmost fully charged, or the like, as well as the electric four-wheeldrive vehicle having no battery. In such cases, there is a need tocontrol the system so as to suppress the regenerative electrical power.

Description will be made below regarding the control processing forhandling the rollback state of the electric four-wheel drive vehicle inwhich the vehicle moves in the direction opposite to the intendeddirection of the travel (which will be referred to as “drivingdirection” hereafter) Description will be made regarding theconfiguration and operation of the electric motor control unit 16included in the electric motor control system according to the presentembodiment with reference to FIG. 3.

FIG. 3 is a block diagram which shows the configuration of the electricmotor control unit included in the electric motor control systemaccording to an embodiment of the present invention.

As shown in FIG. 2, the electric motor control unit 16 comprises therollback determination unit 18, the current instruction computation unit50 for calculating the instruction values for controlling the AC motor 6and the inverter 8, and the capacitor voltage instruction computationunit 51 for calculating the instruction value for controlling thecapacitor voltage.

The rollback determination unit 18 determines the state of the vehiclebased upon the electric motor revolution ωm and the torque instructionTr*. In a case that the torque instruction Tr* is a positive value, andthe electric-motor rotational speed ωm is a negative value, or in a casethat the torque instruction Tr* is a negative value, and theelectric-motor rotational speed ωm is a positive value, determination ismade that the electric motor is rotating in the direction opposite tothe driving direction. That is to say, in such a case, determination ismade that the vehicle is in the rollback state.

The current instruction computation unit 50 includes a currentinstruction computation unit 19, a voltage instruction computation unit20, and a three phase voltage instruction computation unit 21, and aPWM/rectangular-wave-signal processing unit 22. The current instructioncomputation unit 19 calculates the d-axis current instruction Id*,q-axis current instruction Iq*, and field-coil current instruction Imf*,for the synchronous electric motor, based upon the torque instructionTr* and electric motor revolution ωm. For example, the currentinstruction computation unit 50 stores the data of the d-axis current Idand the data of the q-axis current Iq therewithin for each operatingpoint for both the normal state and the rollback state in the form of atable. With such an arrangement, the current instruction computationunit 50 determines the Id* instruction value and the Iq* instructionvalue for each operating point based upon the tables thus stored.Switching between the normal state and the rollback state is performedbased upon the determination result made by the rollback determinationunit 18.

Now, description will be made regarding the control operation of theelectric motor control unit 16 included in the electric motor controlsystem according to the present embodiment with reference to FIG. 4.

FIG. 4 is a flowchart which shows the operation of the electric motorcontrol unit included in the electric motor control system according toan embodiment of the present invention.

First, in Step s101, the electric motor control unit 16 receives theelectric motor revolution ωm as an input signal. Furthermore, in Steps102, the electric motor control unit 16 receives the torque instructionTr* as an input signal.

Next, in Step s103, the rollback determination unit 18 determines thestate of the vehicle based upon the electric motor revolution ωm and thetorque instruction Tr*. Specifically, in a case that the signs of thetorque instruction Tr* and the electric motor revolution ωm areopposite, the rollback determination unit 18 makes a determination ofthe rollback state.

In Step s103, in a case that determination has been made that thevehicle is not in the roll back state, the flow proceeds to Step s104.In Step s104, the current instruction computation unit 19 calculates thecurrent instruction values (Id*, Iq*, Imf*) for controlling the electricmotor and alternator in the normal state, and the flow proceeds to theStep for the processing performed by the voltage instruction computationunit 20.

On the other hand, in Step s103, in a case that determination has beenmade that the vehicle is in the roll back state, the flow proceeds toStep s105. The output of the electric motor in the rollback state isminus, and the electric motor generates regenerative electrical power.Accordingly, in a case that determination has been made that the vehicleis in the rollback state, there is a need to control the system indifferent manner from that employed in the normal mode, so as to absorbthe regenerative energy. First, in Step s105, the current instructioncomputation unit 19 determines whether or not the control operation canbe applied based upon the rollback N-T characteristic.

Now, description will be made regarding the rollback N-T characteristicused by the electric motor control system according to the presentembodiment with reference to FIG. 5.

FIG. 5 is an explanatory diagram for describing the rollback N-Tcharacteristic used by the electric motor control system according to anembodiment of the present invention.

FIG. 5 shows an example of the characteristic of the torque (Nm) withrespect to the electric-motor frequency (Hz). In FIG. 5, the hatchedregions represent the regions where the control operation can be appliedbased upon the rollback N-T characteristic, i.e., the rollback operationregion. With an arrangement employing an electric motor having theelectric motor characteristic as shown in FIG. 5, in a case that theoperating point, i.e., the combination of the torque instruction Tr* andthe electric-motor rotational speed ωm (electric-motor frequency) doesnot fall within the rollback operation region, the flow proceeds to Steps106, whereupon the four-wheel drive controller 32 stops the four-wheeldrive mode.

In Step s105, in a case that determination has been made that theoperating point is within the region where the control operation basedupon the rollback N-T characteristic can be applied, the flow proceedsto Step s107. In Step s107, the output of the generator 4 (which enablesthe electric motor to consume excess electrical power in the form ofelectric motor loss) is determined giving consideration to the enginerevolution (alternator revolution ωg). Specifically, at the time ofdetermining the amount of the driving power to be received from theengine, the most efficient operating point for the output of thegenerator 4 is determined (because the generator [alternator] 4 exhibitsdifferent performance characteristic depending upon the revolution) soas to satisfy the following condition. In a case of the rollback state,the output of the generator 4 is determined such that the electric motorloss is greater than the electric-motor output using the followingmethod. With the effective current applied to the electric motor as I,and with the coil resistance as R, the electric motor loss isrepresented by Expression ((Iˆ2)×R×3). On the other hand, with theelectric-motor rotational speed as ωm, and with the electric motortorque as Tm, the electric-motor output is represented by Expression(ωm×Tm). Here, the electric-motor effective current I is represented bythe following Expression (1) using the d-axis current Id and q-axiscurrent Iq.I=(√(Idˆ2+Iqˆ2))/√3   (1)

Now, description will be made regarding the energy state in the rollbackstate. In a case that the output of the electric motor exceeds theelectric motor loss, the difference in the electrical energytherebetween represents the regenerative energy. An ordinary hybridsystem can use such energy in the regenerative mode. The systemaccording to the present embodiment has no battery, and accordingly,such a system has only a limited capacity for absorbing the electricalenergy. With such an arrangement, the system is preferably controlledsuch that neither an excess nor a shortage of electrical power occurs,i.e., the electric motor loss matches the output of the electric motor.However, it is extremely difficult to control the system such that theelectric motor loss completely matches the output of the electric motor,due to the external factors such as the engine revolution. Accordingly,with the present embodiment, at the time of determining the q-axiscurrent instruction value Iq* according to the torque instruction, theoutput of the electric motor 4 (which enables the electric motor toconsume excess electrical power in the form of electric motor loss) isdetermined such that the electric motor loss ((Iˆ2)×R×3) is greater thanthe electric-motor output (|ωm×Tm|). Furthermore, the d-axis currentinstruction value Id* is determined based upon the calculation results.With the present embodiment, the Id and Iq are prepared for eachrollback operating point with respect to the corresponding enginerevolution, in the form of a table. The d-axis current instruction id*,q-axis current instruction Iq*, and field-current instruction Imf*, arecalculated based upon the table thus prepared. Note that thefield-current instruction Imf* is determined giving consideration to thedriving performance of the vehicle and the motor efficiency.Specifically, the output Pg of the generator 4 is represented by thefollowing Expression (2). Furthermore, the output Pg is determined so asto be greater than zero. The Id*, Iq*, and Imf* are determinedbeforehand based upon the electrical power received from the generator(e.g., 250 W) so as to satisfy the aforementioned condition.((Iˆ2)×R×3)−|ωm×Tm|  (2)

As a result, the excess electrical energy corresponding to the output Pgof the generator 4 is consumed in the form of thermal energy emittedfrom the AC electric motor 6. The aforementioned Id table and Iq tableare created such that the excess electrical energy is applied to the ACelectric motor 6 in the form of ineffective current applied to the ACelectric motor 6. Specifically, the current applied to the magnetic-fluxdirection of the AC electric motor 6 serves as the ineffective current.Upon determination of the excess energy, the flow proceeds to Step s108.In Step s108, the voltage instruction computation unit 20 performscontrol processing for the electric motor and the generator based uponthe current instruction values thus determined.

In FIG. 3, the voltage instruction computation unit 20 calculates thed-axis current instruction Vd* and q-axis voltage instruction Vq* basedupon the d-axis current instruction Id* and q-axis current instructionIq* calculated by the current instruction computation unit 19. Thethree-phase voltage instruction computation unit 21 calculates the ACvoltage instructions Vu*, Vv*, and Vw, for the AC electric motor 6 basedupon the d-axis voltage instruction Vd* and q-axis voltage instructionVq* calculated by the voltage instruction computation unit 20, using themagnetic pole position θ detected by a pole-position sensor included inthe AC electric motor 6. The PWM/rectangular-wave-signal processing unit22 creates a driving signal for the switching devices included in theinverter based upon the AC voltage instructions Vu*, Vv*, and Vw*,output from the three-phase instruction computation unit 21. ThePWM/rectangular-wave-signal processing unit 22 outputs the drivingsignal thus created, to the inverter 8 for performing PWM control orrectangular wave control of the inverter 8.

The capacitor voltage instruction computation unit 51 is a component forcalculating the voltage instruction value for the capacitor 31. Thecapacitor voltage instruction computation unit 51 comprises a DC voltageVdc1 computation unit 23 and a capacitor voltage instruction value Vdc*computation unit 24.

The DC voltage Vdc1 computation unit 23 calculates the output voltage ofthe generator 4, i.e., the voltage Vdc between both terminals of thecapacitor, based upon the d-axis voltage instruction Vd* and the q-axisvoltage instruction Vq* calculated by the voltage instructioncomputation unit 20. First, the phase voltage V applied to the ACelectric motor 6 is calculated using the following Expression (3).V=(√(Vd*ˆ2+Vq*ˆ2))/√3   (3)

Furthermore, in a case of PWM control, the DC voltage Vdc1 computationunit 23 calculates the DC voltage instruction value Vdc1 based upon thephase voltage V applied to the AC electric motor 6 using the followingExpression (4).Vdc1=(2√2)·V   (4)

On the other hand, in a case of the rectangular wave control, the DCvoltage Vdc1 computation unit 23 calculates the DC voltage instructionvalue Vdc1 using the following Expression (5).Vdc1=((2√2)−V)/1.27   (5)

Next, description will be made regarding the operation of the capacitorvoltage instruction value Vdc* computation unit 24 included in theelectric motor control system according to the present embodiment withreference to FIG. 6.

FIG. 6 is a flowchart which shows the operation of the capacitor voltageinstruction value Vdc* computation unit included in the electric motorcontrol system according to an embodiment of the present invention.

In Step s120, the capacitor voltage instruction value Vdc* computationunit 24 extracts the operating point where the generator 4 generates theoutput voltage Vdc1 at the revolution ωg of the engine 3. With thepresent embodiment, a reduction mechanism is provided between the engine3 and the generator 4. With such an arrangement, the engine revolutionωg of 600 rpm is converted into the generator revolution ωg′ of 1500 rpmat a reduction ratio of 2.5, for example.

Now, description will be made regarding the characteristics of thegenerator 4 (at the revolution ωg′) with reference to FIG. 7.

FIG. 7 is an explanatory diagram for describing the characteristic ofthe generator.

Let us say that the generator 4 has the characteristics (at therevolution ωg′) as shown in FIG. 7. The capacitor voltage instructionvalue Vdc* computation unit 24 extracts the operating point where thegenerator 4 generates the output voltage Vdc1 at the engine revolutionωg (i.e., at the generator revolution ωg′), i.e., the output currentIdc1 of the generator 4, using the table as shown in FIG. 7.

Next, in Step s121 shown in FIG. 6, the capacitor voltage instructionvalue Vdc* computation unit 24 determines whether or not the AC electricmotor 6, driven by receiving the output voltage Vdc1 and the outputcurrent Idc1 from the generator 4, can satisfy the requested electricmotor torque Pm (=electric motor revolution ωm× torque instruction Tr*).

In a case that the operating point of the generator 4 satisfies therequested need for power, the flow proceeds to Step s122. The capacitorvoltage instruction value Vdc* computation unit 24 calculates theoptimum voltage instruction value Vdc2 based upon the DC voltageinstruction value Vdc1, which enables the effective operation of the ACelectric motor 6 and the generator 4. Next, in Step s123, the capacitorvoltage instruction value Vdc* computation unit 24 outputs the voltageinstruction value Vdc2 to the generator control unit 17 shown in FIG. 2,as the voltage instruction value Vdc*.

On the other hand, let us consider a case in which determination hasbeen made that the operating point of the generator 4 does not satisfythe requested need for power, in Step s121. In this case, in Step s124,the capacitor voltage instruction value Vdc* computation unit 24calculates the voltage instruction value Vdc3 and the torque instructionvalue Tr* so as to output the requested power. Next, in Step s125, thecapacitor voltage instruction value Vdc* computation unit 24 outputs thevoltage instruction value Vdc3 to the generator control unit 17 shown inFIG. 2, as the voltage instruction value Vdc*.

Next, description will be made regarding the generator control methodfor the generator 4, employed in the electric motor control systemaccording to the present embodiment with reference to FIGS. 8 and 9.Here, description will be made regarding a control method in which theDC bus voltage is used as a feedback signal, as an example.

FIG. 8 is a block diagram which shows the configuration of the generatorcontrol unit 17 included in the electric motor control system accordingto an embodiment of the present invention. FIG. 9 is a flowchart whichshows the operation of the generator control unit included in theelectric motor control system according to an embodiment of the presentinvention.

As shown in FIG. 8, the generator control unit 17 includes subtractionmeans 27, a voltage feedback control unit 25, and a Duty (C1)computation unit 26.

In Step s122 shown in FIG. 9, the subtraction means 27 calculate thedeviation ΔVdc between the capacitor voltage instruction value Vdc*output from the electric motor control unit 16 and the capacitor voltageVdc which is the voltage applied to both electrodes of the capacitor.

Next, in Step s112, the voltage feedback control unit 25 performsproportional integration (PI) for the deviation ΔVdc obtained in Steps111, and outputs the field-voltage instruction Vgf*. While descriptionhas been made regarding an arrangement employing the PI control, thepresent invention is not restricted to such an arrangement. Let usconsider a case in which such an arrangement employing the feedbackcontrol system alone has poor response performance. In order to solvethe aforementioned problem, an arrangement may be made employingfeedforward compensation, in addition to the feedback control.

Next, in Step s113, the Duty (C1) computation unit 26 calculatesVgf*/Vdc as the duty C1(Vgf*) based upon the field-voltage instructionVgf* output from the voltage feedback control unit 25. The duty C1(Vgf*)signal thus calculated by the Duty (C1) computation unit 26 is suppliedto the field coil of the generator 4 so as to perform feedback controlsuch that the capacitor voltage Vdc applied to both terminals of thecapacitor 31 matches the capacitor voltage instruction value Vdc*.

As described above, the present embodiment provides stable control ofthe capacitor voltage Vdc according to the voltage instruction Vdc*.This enables power control for the mutually supportive operation in acooperative manner between the cooperative operation of the generator 4,the electric motor, and the inverter. Here, the voltage instruction Vdc*is determined based upon the operating point (electric motor revolution,electric motor torque) of the AC electric motor 6.

Next, description will be made regarding the control operation of theelectric four-wheel drive vehicle 1 employing the electric motor controlsystem according to the present embodiment with reference to FIG. 10.Here, description will be made regarding the control operation in therollback state.

FIGS. 10A through 10C are timing charts which show the control operationfor the electric four-wheel drive vehicle 1 employing the electric motorcontrol system according to an embodiment of the present invention. FIG.10A shows the electric motor torque Tm. FIG. 10B shows theelectric-motor rotational speed o)m. FIG. 10C shows the capacitorvoltage Vdc. In each drawing, the horizontal axis represents time (sec).

As shown in FIGS. 10A and 10B, in the rollback state, while the electricmotor torque is a positive value, the electric-motor rotational speed isa negative value. As described above, the output of the generator 4 isdetermined such that the electric motor loss ((Iˆ2)×R×3) is greater thanthe electric-motor output (|ωm×Tm|). With such an arrangement, the usualperspective would be that the excess energy supplied to the electricmotor in the rollback state should be set to a necessary minimum valuein order to reduce the energy loss as much as possible. However, withthe present embodiment, the excess energy supplied to the electric motorin the rollback state is set to a value somewhat greater than thenecessary minimum value. The reason is as follows. Let us consider acase in which the generator 4 outputs the necessary minimum electricalpower in the rollback state. In this case, the generator 4 cannot supplysufficient electrical power for the output of the requested torque inthe normal mode immediately after the rollback state. In contrast tosuch an arrangement, with the present embodiment, the generator 4outputs electrical power somewhat greater than the necessary minimumelectrical power in the rollback state for handling such a situation.This enables the system according to the present embodiment to outputthe necessary torque in the normal mode immediately after the recoveryfrom the rollback state. The electrical power thus determined is inputto the AC electric motor 6, and is consumed in the form of electricalpower loss. This enables the capacitor voltage Vdc to be stablycontrolled throughout a period of time from the rollback state up to thenormal operation mode after the recovery from the rollback state asshown in FIG. 10C.

As shown in FIG. 10B, upon the recovery from the rollback state, therotational speed of the electric motor changes from a negative value toa positive value, i.e., the vehicle is driven in the power running modewhich is a normal driving mode. However, in some cases, the rotationalspeed of the electric motor temporarily changes from a positive value toa negative value in a pulsed manner, as shown in FIG. 10B. In order tosolve this problem, with the present embodiment, in a case that therotational speed of the electric motor changes from a positive value toa negative value after the recovery from the rollback state to the powerrunning mode, determination is made whether this change in therotational speed of the electric motor has occurred in a pulsed manner,or due to the rollback state. In a case that the negative rotationalspeed of the electric motor o)a has been detected as shown in FIG. 10B,the absolute value of ωa thus detected is compared with a threshold ωaX.In a case that |ωa|<ωaX, the rollback determination unit 18 does notmake a determination that the vehicle is in the rollback state. Thethreshold ωaX is set to 50 [rpm], for example. With such an arrangement,in Step s103 shown in FIG. 4, in a case that the rotational speed of theelectric motor satisfies the condition of ↑ωa|<ωaX as described above,the flow proceeds to Step s104.

As described above, the present embodiment enables an electricfour-wheel drive vehicle having no battery to output the requestedtorque while absorbing the regenerative electrical power which is excesselectrical energy. This allows such an electric four-wheel drive vehicleto output the requested torque while preventing damage to the capacitor31 and the power devices included in the inverter 8 due to theregenerative electrical power. Also, the present embodiment may beapplied to an arrangement employing a field-coil synchronous electricmotor as the AC electric motor. This enables effective torque controland power generation control by adjustment of the field current. Notethat the control method according to the present embodiment can beeffectively performed at the time of shift change, or in order to escapefrom the mud.

Next, description will be made regarding the configuration and operationof an arrangement in which an electric motor control system according toanother embodiment of the present invention is applied to a hybridvehicle having a simple configuration employing an AC electric motor andan AC generator with reference to FIG. 11.

FIG. 11 is a system block diagram which shows an overall configurationof an arrangement in which an electric motor control system according toan embodiment of the present invention is applied to a hybrid vehiclehaving a simple configuration employing an AC electric motor and an ACgenerator (alternator). Note that the same components as those shown inFIG. 1 are denoted by the same reference numerals.

The electric four-wheel drive vehicle shown in FIG. 1 has no battery,and the small electrical power stored in the capacitor 31 included inthe inverter 8 needs to be controlled. On the other hand, with thepresent embodiment, a hybrid vehicle includes a battery 200 as shown inFIG. 11. With such an arrangement, the electrical power generated by thegenerator 4 can be stored in the battery 200. Specifically, the battery200 temporarily stores the electrical power generated by the generator4, and accumulates the regenerative electrical power. In a case that thevehicle is in the rollback state as described above, the regenerativeelectrical power is accumulated in the battery 200.

With the present embodiment, an electric motor controller 14A monitorsthe charge state of the battery 200. In a case that determination hasbeen made that the battery 200 cannot absorb the regenerative energygenerated by the AC electric motor 6, the electric motor controller 14Aeffects control so as to suppress the regenerative electrical power.That is to say, in a case that it is difficult to absorb theregenerative electrical power as described above, the excessregenerative energy should be consumed by they AC electric motor.Accordingly, basic control is performed such that the electric-motoroutput matches the electric motor loss, i.e., Pg=0 as introduced fromExpression (2). Let us consider a situation in which the battery 200cannot store regenerative electrical power, in the same way as theelectric four-wheel drive vehicle 1 shown in FIG. 1. In this situation,with the present embodiment, the output of the generator (which enablesthe electric motor to consume excess electrical power in the form ofelectric motor loss) is determined such that the electric motor loss isgreater than the output of the electric-motor, giving consideration tothe engine revolution ωg. This enables the AC electric motor 6 toconsume the excess electrical energy, which cannot be absorbed by thebattery 200, in the form of thermal energy. As described above, thepresent embodiment can be applied to a hybrid vehicle having aconfiguration employing an AC generator as the generator. Such anarrangement has the advantage of effectively consuming excessregenerative energy.

Next, description will be made regarding to the configuration andoperation of an arrangement in which an electric motor control systemaccording to yet another embodiment of the present invention is appliedto a hybrid vehicle employing a motor generator 4B as the generator,with reference to FIG. 12.

FIG. 12 is a system block diagram which shows an overall configurationof an arrangement in which an electric motor control system according toyet another embodiment of the present invention is applied to a hybridvehicle employing the motor generator 4B as the generator. Note that thesame components as those shown in FIG. 1 are denoted by the samereference numerals.

Unlike an alternator, the motor generator 4B has both the generatingfunction and driving function. Accordingly, an electric-power converter10B such as an inverter is provided. Note that the same components asthose shown in FIG. 1 are denoted by the same reference numerals. Withthe hybrid vehicle having such a configuration, the regenerativeelectrical power is accumulated in the battery 200 in the rollback stateof the vehicle in the same way as described above. With such anarrangement, the electric motor controller 14A monitors the charge stateof the battery 200. In a case that determination has been made that thebattery 200 cannot absorb the regenerative energy generated by the ACelectric motor 6, the system is controlled so as to suppressregenerative electrical power. That is to say, in a case that it isdifficult for the battery 200 to absorb the regenerative electricalpower, the excess regenerative energy should be consumed by the ACelectric motor. Accordingly, with such an arrangement, basic control isperformed such that the output of the electric motor matches theelectric motor loss, i.e., Pg=0 as introduced from Expression (2), asdescribed above.

Let us consider a case in which the battery 200 has a certain degree ofavailable capacity, unlike a situation in which the battery 200 is fullycharged or almost fully charged. An arrangement may be made in whichdetermination is made that the battery 200 has been fully charged fromsuch a battery-charge state, depending upon other factors which cause alarge amount of current in an extremely short period of time. Forexample, let us consider a situation in which the vehicle takes offuphill on a slippery slope, or a case of escaping from deep snow or mud.In such cases, the driver presses the accelerator pedal withconsiderable force. This increases the engine revolution and the torqueinstruction. In such cases, the generator generates an excess of energyas the regenerative electrical power. In some cases, determination canbe made that the quantity of such electrical power is too large to bestored in the battery 200 since the generator generates a considerablylarge amount of regenerative electrical power. Accordingly, anarrangement may be made in which a part of the regenerative electricalpower is accumulated in the battery 200, and the remaining part isconsumed by the AC electric motor 6 in the form of thermal energy. Suchan arrangement enables effective control of the charging/discharging ofthe battery 200.

1. A control system for an electric driving system for a vehicle,comprising: an inverter for converting a DC electrical power output,from a capacitor capable of electrical charge and discharge of electricpower, into AC electrical power; and an AC electric motor, driven by theAC electrical power output from said inverter for generating electricaldriving force for driving a component to be driven, wherein said controlsystem for an electric driving system controls driving of said ACelectric motor by controlling said inverter according to an instructedtorque for said AC electric motor, and wherein, with said capacitor ator near a state of full charge or near it and the output of said ACelectric motor becomes negative, and excess electrical energy isgenerated, said control system controls the current applied to said ACelectric motor such that the loss in said AC electric motor exceeds thenegative output of said AC electric motor.
 2. A control system for anelectric driving system according to claim 1, wherein in a case that theoutput of said AC electric motor becomes negative, and excess electricalenergy is generated, said control system controls the current applied tosaid AC electric motor so as to increase ineffective current in said ACelectric motor.
 3. A control system for an electric driving systemaccording to claim 2, wherein the ineffective current in said ACelectric motor, which is absorbed in the form of loss in said ACelectric motor, is determined based upon the excess electrical poweroutput to said inverter from said in-vehicle power supply.
 4. A controlsystem for an electric driving system for a vehicle, wherein saidelectric driving system for a vehicle comprising: an inverter forconverting a DC electrical power output, from a capacitor capable ofelectrical charge and discharge of electric power, into AC electricalpower; and an AC electric motor driven by the AC electrical power outputfrom said inverter for driving at least one of said plurality of wheelsother than said wheels driven by said internal combustion engine,wherein said control system for an electric driving system controlsdriving of said AC electric motor by controlling said inverter accordingto an instructed torque received from a vehicle for said AC electricmotor, and wherein, with said capacitor not at or near a state of fullcharge, a split-second large current which the output of said ACelectric motor becomes negative is generated, said capacitor cannotaccept all electric energy, and the output of said AC electric motorbecomes negative, and excess electrical energy is generated, saidcontrol system controlling the current applied to said AC electric motorsuch that the loss in said AC electric motor exceeds the negative outputof said AC electric motor.
 5. A control system for an electric drivingsystem according to claim 4, wherein, with the output of said ACelectric motor becoming negative, and excess electrical energy beinggenerated, said control system controls the current applied to said ACelectric motor so as to increase ineffective current in said AC electricmotor.
 6. A control system for an electric driving system according toclaim 5, wherein the ineffective current in said AC electric motor,which is absorbed in the form of loss in said AC electric motor, isdetermined based upon the excess electrical power output to saidinverter from said generator.
 7. A control system for an electricdriving system which drives a vehicle by electro-moving force comprises:an inverter for converting a DC electrical power output from a capacitorin which electrical charge and discharge of electric power is possible,into AC electrical power; and an AC electric motor, which is driven bythe AC electrical power output from said inverter, for generatingelectrical driving force for driving said vehicle, wherein said controlsystem for an electric driving system includes controlling driving ofsaid AC electric motor by controlling said inverter according to aninstructed torque received from a vehicle for said AC electric motor,and wherein, with said capacitor at or near a state of full charge andthe output of said AC electric motor becomes negative, and excesselectrical energy is generated, said controls system controlling thecurrent applied to said AC electric motor such that the loss in said ACelectric motor exceeds the negative output of said AC electric motor. 8.A control system for an electric driving system according to claim 7,wherein, with the output of said AC electric motor becoming negative,and excess electrical energy being generated, said control systemcontrols the current applied to said AC electric motor so as to increaseineffective current in said AC electric motor.
 9. A control system foran electric driving system according to claim 8, wherein the ineffectivecurrent in said AC electric motor, which is absorbed in the form of lossin said AC electric motor, is determined based upon the excesselectrical power output to said inverter from said capacitor.
 10. Acontrol system for an electric driving system for a vehicle, comprising:an inverter for converting a DC electrical power output from a capacitorcapable of electrical charge and discharge of electric power into ACelectrical power; and an AC electric motor driven by the AC electricalpower output from said inverter, for generating electrical drivingforce; and a control unit for controlling driving of said AC electricmotor by controlling said inverter according to an instructed torque forsaid AC electric motor wherein, with said capacitor not at or near astate of full charge, a split-second large current which the output ofsaid AC electric motor becomes negative is generated, said capacitorcannot finish accepting all electric energy, and the output of said ACelectric motor becomes negative, and excess electrical energy isgenerated, said control unit being configured to control the currentapplied to said AC electric motor such that the loss in said AC electricmotor exceeds the negative output of said AC electric motor, and whereinthe excess electrical power is supplied to said inverter from saidin-vehicle power supply in the form of loss in said AC electric motor.11. An electric driving system for an electric driving system accordingto claim 10, wherein, with the output of said AC electric motor becomingnegative, and excess electrical energy is generated, said control unitcontrols the current applied to said AC electric motor so as to increaseineffective current in said AC electric motor.
 12. An electric drivingsystem for an electric driving system according to claim 11, wherein theineffective current in said AC electric motor is determined based uponthe excess electrical power.
 13. A hybrid vehicle comprising: aninternal combustion engine for generating driving force for a vehicle;an AC electric motor for generating driving force for said vehicle; acapacitor forming a power supply for said AC electric motor; an inverterfor converting DC electrical power received from said capacitor, into ACelectrical power, which is supplied to said AC electric motor fordriving said AC electric motor; and a control device for controllingdriving of said AC electric motor by controlling said inverter accordingto an instructed torque received from a vehicle for said AC electricmotor, wherein, with said capacitor at nor near a state of full chargeand the output of said AC electric motor becoming negative, and excesselectrical energy is generated, said control device controls the currentapplied to said AC electric motor such that the loss in said AC electricmotor exceeds the negative output of said AC electric motor, and whereinthe excess electrical power is supplied to said inverter from saidcapacitor in the form of loss in said AC electric motor.
 14. A hybridvehicle comprising: an internal combustion engine for generating drivingforce for a vehicle; an AC electric motor for generating driving forcefor said vehicle; a capacitor forming a power supply for said ACelectric motor; an inverter for converting DC electrical power receivedfrom said capacitor, into AC electrical power, which is supplied to saidAC electric motor for driving said AC electric motor; and a controldevice including control means for controlling driving of said ACelectric motor by controlling said inverter according to an instructedtorque received from a vehicle for said AC electric motor, and wherein,with said capacitor not at or near a state of full charge, asplit-second large current which the output of said AC electric motorbecomes negative is generated, said capacitor cannot accept all electricenergy, and the output of said AC electric motor becomes negative, andexcess electrical energy is generated, said control device controls thecurrent applied to said AC electric motor such that the loss in said ACelectric motor exceeds the negative output of said AC electric motor.